Sandwiches of magnetorheological elastomer (SMRE), already known, are composed of aluminium skins due to their low damping and to their high rigidity as compared to MREs. Moreover, the relative magnetic permeability of aluminium is almost nil; thus, it does not affect the distribution and intensity of the magnetic field.
The core of the SMREs is composed mainly of a polymeric matrix and magnetic particles. The matrix used by the different authors to manufacture the MRE are Selleys Pty. Limited silicone with Polydimethylsiloxane fluid, Liyang Silicone Rubber, the inorganic polymer Bentonite Clay and synthetic oil and silicone Elastosil M4644. As magnetic particles, the most used is that of carbonyl iron (C5FeO5), with a diameter of more than 3 μm and in a proportion of 25-30% in volume of the MRE.
For the bonding of the polymeric matrix to the skins, an adhesive is used.
In the known SMREs the ratio of the skin thickness to the thickness of the core varies from 1.1% to 20%; that is, the core is always much thicker than the skins.
This configuration carries with it several problems.
The known SMRE are very expensive products.
They also present the problem of being excessively thick, which makes their application difficult precisely in the structures where, due to their high added value, such as in aviation or automobiles, their use is very desirable.
In structures that require a folding of the SMRE of more than 90° we have checked the tendency to peel off, due to the excessive thickness of the sandwich.
The need for the adhesive to join the core with the skins has as a result a more complex preparation of SMRE and consequently, a more expensive preparation.
These and other problems are solved by the SMRE that is the object of the invention.